Description

When I try to create a gist from a file or stdin, containing only whitespace, I get a 422 validation failed error.

This can be reproduced in gh versions 1.8.1 and 1.9.2

Steps to reproduce the behavior

echo $' \t' | gh gist create
- Creating gist...
X Failed to create gist: HTTP 422: Validation Failed (https://api.github.com/gists)
Gist.files is missing

Expected vs actual behavior

I expect to see a message that reports "unable to create a gist from an empty file".